The present invention relates to parallel processing systems and more particularly to a method for cooperatively managing resources on a system employing a group of processors, each of which is provided with a respective section of memory which is also accessible by other processors in the group.
When a variety of processes may be running simultaneously e.g., in a multi-tasking or time-sharing environment, it is known that some method or technique must be provided for preventing interference between different processes seeking access to the same resource. Resources may, for example, be files, portions of a data base, or physical entities such as a printer or display screen.
As is understood by those skilled in the art, the extent of access which one process requires with respect to a given resource, may change very frequently. This is done so that high level or exclusive levels of access are existent only for as short a time as possible, since high levels of access effectively exclude other processors. On the other hand, multiple processes can typically have simultaneous access at low levels, such as read only in the case of files.
In the prior art, various systems have been developed, such as file and record locking schemes, for implementing appropriate protections on single-processor systems. Certain locking schemes have also been extended to systems comprising small numbers of processors. For example, Digital Equipment Corporation of Maynard, Mass. provides a VMS lock manager system for protecting resources in its VAX line of computers when such computers are operated in clusters. Typically, however, the data managed by the lock manager system runs is tied to the memory of that one of the computers which first identified a given resource and processes running on other processors must access that data by means of a message passing scheme in order to effect any claim for access rights to the resource.
As will be perceived by those skilled in the art, a lock manager system which depends heavily on a single or master processor, will be very inefficient when the number of processors becomes large since the lock manager itself, together with its data, will be a hot spot or source of contention amongst various processes running on many different processors. Stated another way, such schemes do not permit linear growth or graceful scaling of performance in relation to the number of processors.
As is also understood, there is increasing interest in massively parallel processors, i.e. computer systems in which very large numbers of processors are employed, since it is increasingly difficult to improve the power or capability of single-processors due to physical limits.
Among the several objects of the present invention may be noted the provision of a novel method for managing resource in a multi-processor computer system, the provision of such a method which scales gracefully; the provision of such a method which operates effectively with relatively large numbers o processors; the provision of such a method in which resource management data is distributed over the system memory; the provision of such a method which automatically provides updated request status information to processors seeking a resource; the provision of such a method which is highly reliable, which operates effectively and which is of relatively simple and inexpensive implementation. Other objects and features will be in part apparent and in part pointed out hereinafter.